An NYC hostess who has been accused of being Jay Z’s mistress is fighting back the rumor. Casey Cohen says she has never been intimate with the rapper/mogul and is demanding that magazines that said she slept with Hova need to issue and apology, or else she’s suing.

Casey Cohen — who was on the Bravo show “Princesses: Long Island” — was named as Jay’s alleged side piece in several magazines (such as In Touch) … all owned by Bauer Media Group.

TMZ has learned Cohen has hired a lawyer who fired off a cease and desist letter saying Cohen and Jay Z “have never been in love or intimate” — and dismissing all the Bauer articles as “a foul and phony mistress-rumor.”

Cohen cops to having met Jay Z and Beyonce several times — in the letter, obtained by TMZ — but only through her job working as a VIP hostess in New York City.

She is demanding Bauer issue a public apology to her, Jay Z, and Beyonce … and remove all posts about her from the Internet.